Mask for sputtering

ABSTRACT

In a sputtering process of forming a transparent electrode film ( 13 ) on a color filter ( 14 ), the dielectric breakdown of a peripheral portion of the color pattern film ( 10 )due to abnormal discharge is prevented. A metal mask ( 8 ) has a mask body ( 8   b ) provided with openings ( 8   a ) having a shape corresponding to that of the color pattern films ( 10 ) formed on a glass substrate ( 9 ) Stepped portions ( 8   d ) are formed by recessing brim portions ( 8   c ) of the openings ( 8   a ) facing the color filters ( 14 ). Gaps ( 11 ) are formed between the mask body ( 8   b ) and peripheral portions of the color pattern films ( 10 ) of the color filters ( 14 ). The mask body ( 8   b ) is provided on the stepped portions ( 8   d ) with conductive projections ( 12 ). The conductive projections ( 12 ) come into electrical contact with black shading strips ( 10   b ) formed in the peripheral portions of the color pattern films ( 10 ) of the color filters ( 14 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a color filter for a liquid crystaldisplay or the like. More particularly, the present invention relates toa mask for sputtering to be used for forming a transparent electrodelayer on a color filter by sputtering, a sputtering process, a colorfilter provided with a transparent electrode layer formed by thesputtering process using the mask for sputtering.

2. Description of the Related Art

A color filter fabricating method includes a chromium film formingprocess for forming a chromium film on a glass substrate by a vacuumevaporation method; a black shading layer forming process for forming ablack shading layer of a striped pattern having stripes or a latticedpattern having crisscrossed stripes by coating the chromium film with aphotoresist film, placing a photomask on the photoresist film, exposingthe photoresist film through the photomask to light and developing theexposed photoresist film, etching the chromium film through the exposedphotoresist film, and removing the exposed photoresist film; RGB colorlayer forming process for forming R, G and B color layers; and atransparent electrode forming process for forming a transparentelectrode layer by forming an indium tin oxide film (ITO film) on the R.G and B color layers. The RGB color layer forming process includes thestep of forming a first color layer by spreading a first coloringphotosensitive material in a first color film over the black shadinglayer, placing a photomask on the first color film, exposing the firstcolor film to light through the photomask and developing the exposedfirst color film, and steps of forming a second and a third color layer,similar to the step of forming the first color layer.

A sputtering method is used prevalently in the transparent electrodeforming process because the sputtering method is capable of forming asufficiently adhesive thin film of a uniform thickness at acomparatively low temperature in a short time. In an automatedproduction line, a combination of a glass substrate provided with ablack shading layer and the color layers, and a sputtering mask isfixedly held in a jig, and several tens of such jigs are carried into asputtering apparatus, and the glass substrates held in the jigs aresubjected to a sputtering process.

FIG. 2 shows a sputtering jig disclosed in JP-A No. 117839/1993 in anexploded perspective view. The sputtering jig 1 has a substrate holdingplate 2 provided with an opening 2 a, and a substrate fastening plate 5connected to the substrate holding plate 2 by a hinge 3 so as to beturnable relative to the substrate holding plate 2. A plurality ofmagnets 6 are embedded in the substrate fastening plate 5. A pluralityof guide pins 7 are arranged on the substrate holding plate 2 around theopening 2 a. A mask 8 and a glass substrate 9 are set in place on thesubstrate holding plate 2 by setting the mask 8 and the glass substrate9 in contact with the guide pins 7. After setting the mask 8 and theglass substrate 9 on the substrate holding plate 2, the substratefastening plate 5 is turned relative to the substrate holding plate 2 tohold fixedly the mask 8 and the glass substrate 9 between the substrateholding plate 2 and the Lifer substrate fastening plate 5. The glasssubstrate 9 is provided with a plurality of color pattern films 10, andthe mask 8 is provided with openings 8 a of a shape corresponding tothat of the color patterns 10 on the glass substrate 9. The mask 8 isformed of a heat-resistant ferromagnetic material capable ofwithstanding a high temperature on the order of 200° C.

In the jig 1, the mask 8 of a ferromagnetic material is attracted firmlyto the substrate fastening plate 5 by the magnets 6 of the substratefastening plate 5 so that the mask 8 is in close contact with the glasssubstrate 9. When the mask 8 and the glass substrate 9 thus firmlyjoined together are exposed to a high temperature on the order of 200°C. in the sputtering apparatus, thermal stresses are induced in the mask8 and the glass substrate 9 due to difference in coefficient of thermalexpansion between the mask 8 and the glass substrate 9. Consequently,peripheral portions (black shading strips 10 b) of the color patternfilms 10 formed on the glass substrate 9 are liable to be damaged, andliquid crystal displays provided with color filters thus fabricated areliable to be defective due to the leakage of light thrown by abacklight.

A sputtering jig is proposed to solve such a problem in JP-A No.88206/1994. When this prior art sputtering jig is used, recesses areformed in brim portions of the openings 8 a of the mask 8 (FIG. 2)facing the glass substrate 9 by etching so that clearances are securedbetween the mask 8 and the circumferences of the color pattern films 10formed on the glass substrate 9 to prevent damaging peripheral portionsof the color pattern films 10.

A sputtering apparatus that processes the glass substrate 9 held by thesputtering jig has a vacuum vessel filled with a gas. A negative voltageis applied to a target placed in the vacuum vessel to produce a plasmaby ionizing the gas by electric discharge, and a transparent electrodelayer is deposited on the color pattern films 10 by bombarding thetarget with ions of the plasma to cause the target sputter atoms fromits bombarded surface. When a gap 11 is formed between the mask 8 andthe glass substrate 9 as shown in FIG. 3, a relatively amount ofelectric charges is accumulated on the surface of the mask 8 due tosecondary electron emission because the mask 8 and the glass substrate 9are exposed to electric discharge. Therefore, abnormal electricdischarge from the mask 8 to the glass substrate 9 occurs when thepotential difference between the mask 8 and the glass substrate 9increases to a certain level. Consequently, breaks F are formed inperipheral portions (black shading strips 10 b) of the color patternfilms 10 formed on the glass substrate 9 due to dielectric breakdown.

SUMMARY OF THE INVENTION

The present invention has been made in view of those problems and it istherefore an object of the present invention to provide a sputteringmask, a color filter and a sputtering method used for forming atransparent electrode layer on a color filter by sputtering, capable ofpreventing the formation of breaks in a peripheral portion of a colorpattern film due to dielectric breakdown caused by abnormal discharge.

According to a first aspect of the present invention, a sputtering maskfor forming a transparent electrode film on a color filter bysputtering, comprises: a mask body provided with an opening having ashape corresponding to that of a color pattern film of the color filter,and a gap forming portion formed by recessing a brim portion of theopening facing the color filter; and a conductive part formed in the gapforming portion so as to be in electrical contact with a conductiveshading strip formed in a peripheral portion of the color pattern film.Preferably, the gap forming portion is a stepped portion extending alongthe brim portion of the opening of the mask body. Also, it is preferredthat the conductive part is a conductive projection projecting from thegap forming portion of the mask body.

According to a second aspect of the present invention, a color filter onwhich a transparent electrode layer is formed by sputtering using asputtering mask, comprises a glass substrate; a color pattern filmformed on the glass substrate; and a conductive part formed on aconductive shading strip formed in a peripheral portion of the colorpattern film so as to be in electrical contact with the sputtering mask.Preferably, the conductive part is a conductive projection projectingfrom the conductive shading strip.

According to a third aspect of the present invention, a sputteringmethod of forming a transparent electrode film on a color filter bysputtering, comprises the steps of: preparing a sputtering mask providedwith an opening having a shape corresponding to that of a color patternfilm of the color filter; placing the sputtering mask on the colorfilter so that the opening of the sputtering mask coincide with thecolor pattern film and a gap is formed between a brim portion of theopening of the sputtering mask and a peripheral portion of the colorpattern film of the color filter; and forming a transparent electrodelayer by sputtering using the sputtering mask on the color filter withthe sputtering mask electrically connected to a conductive shading stripformed in the peripheral portion of the color pattern film by aconductive part.

According to the present invention, the sputtering mask and the colorfilter (glass substrate) are kept in electrical contact with each otherby the conductive part and the conductive shading layer. Therefore,there is no potential difference between the sputtering mask and thecolor filter (glass substrate) even if the sputtering mask and the colorfilter are charged, so that it is possible to prevent the formation ofbreaks in the peripheral portion of the color pattern due to dielectricbreakdown caused by abnormal discharge.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C are views of assistance in explaining a sputtering maskin a preferred embodiment of the present invention, in which FIG. 1A isa plan view of the sputtering mask, FIG. 1B is an enlarged plan view ofa portion IB of the sputtering mask shown in FIG. 1A as superposed on acolor filter in process, and FIG. 1C is a sectional view taken on lineIC—IC in FIG. 1B;

FIG. 2 is an exploded perspective view of a sputtering jig; and

FIG. 3 is a view of assistance in explaining a problem to be solved bythe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1A, a metal mask (a sputtering mask) 8 in a preferredembodiment of the present invention has a mask body 8 b provided with aplurality of openings 8 a. The mask body 8 b is formed of aheat-resistant ferromagnetic material capable of withstanding hightemperatures on the order of 200° C., such as a nickel-iron alloy.Preferably, the mask body 8 b is formed of an alloy having a coefficientof thermal expansion nearly equal to that of a glass substrate 9, suchas a stainless steel (SUS402, JIS). More preferably, the mask body 8 bis formed of an alloy containing 42% nickel.

The metal mask 8 is used for forming transparent electrode layers 13 bysputtering on color filters 14, respectively. As shown in FIG. 1C, eachof the openings 8 a of the mask body 8 b has a shape corresponding tothat a color pattern film 10 of each color filter 14.

As shown in FIGS. 1B and 1C, the color filter 14 includes a glasssubstrate 9 and the color pattern film 10. The color pattern film 10 hasa latticed pattern of black shading strips 10 b and a color layer 10 asurrounded by the latticed black shading strips 10 b. In FIGS. 1B and1C, only a portion of the black shading strips 10 b in a peripheralportion of the color pattern film 10, and only one of the color layers10 a in the same peripheral portion of the color pattern film 10 areshown. The black shading strips 10 b are formed of a conductivematerial, such as chromium.

As shown in FIGS. 1B and 1C, each opening 8 a of the mask body 8 b isformed so that the brim portion 8 c thereof covers about half the widthof the black shading strips 10 b surrounding the color layer 10 a of thecolor pattern film 10 of the color filter 14. As shown in FIG. 1B, aprojection 8 e, i.e., a terminal, is formed in a corner of each opening8 a of the mask body 8 b . When the metal mask 8 thus formed is used fordepositing an indium tin oxide film (ITO film) on the color filter 14 bysputtering, a transparent electrode layer 13 of a shape represented by ashaded area in FIG. 1B is formed.

Stepped portions (gap forming portions) 8 d are formed in the brimportion 8 c of each opening 8 a of the mask body 8 b, facing the colorfilter 14 to form a gap 11 between the mask body 8 b and peripheralportions of the color pattern film 10. The stepped portions 8 d of themask body 8 b can be formed by half-etching the brim portions 8 c of theopenings 8 a.

As shown in FIGS. 1A and 1B, the stepped portions 8 d of the mask body 8b are provided with conductive projections 12 formed so as to overlapand to be in electrical contact with the black shading strips 10 b. Thewidth d of portions of the conductive projections 12 overlapping theblack shading strips 10 b is on the order of 0.2 mm.

The conductive projections 12 are formed by half-etching the brimportions 8 c of the openings 8 a of the mask body 8 b excluding portionscorresponding to the conductive projections 12 when forming the steppedportions 8 d. The conductive projections 12 may be formed by othermethods.

Although the metal mask 8 may be provided with at least one conductiveprojection 12, it is preferable to form the plurality of conductiveprojections 12 (three conductive projections 12 in FIG. 1A) around eachof the openings 8 a of the mask body 8 b in an arrangement as shown inFIG. 1A, because the width d of the portions of the conductiveprojections 12 overlapping the black shading strips 10 b is as small asabout 0.2 mm and hence it is possible that the conductive projections 12cannot be satisfactorily in electrical contact with the black shadingstrips 10 b if errors in the position of the black shading strips 10 bis, for example on the order of 0.5 mm. However, when the plurality ofconductive projections 12 are arranged as shown in FIG. 1A, some of theconductive projections 12 can be surely in electrical contact with someof the black shading strips 10 b even if the black shading strips 10 bare dislocated linearly or angularly.

A sputtering method of forming the transparent electrode layer 13 on thecolor filter 14 that uses the metal mask 8 will be describedhereinafter.

The metal mask 8 provided with the plurality openings 8 a of a shapecorresponding to that of the color pattern film 10 is prepared. Themetal mask 8 is placed on the color filter 14 by using the sputteringjig I shown in FIG. 2. The sputtering jig 1 has the substrate holdingplate 2 provided with the opening 2 a, and the substrate fastening plate5 connected to the substrate holding plate 2 by the hinge 3 so as to beturnable relative to the substrate holding plate 2. The plurality ofmagnets 6 are embedded in the substrate fastening plate 5.

More concretely, the mask 8 and the color filter 14 (the glass substrate9) are set in place on the substrate holding plate 2 by setting the mask8 and the color filter 14 in contact with the guide pins 7 arrangedaround the opening 2 a of the substrate holding plate 2 of thesputtering jig 1. After setting the mask 8 and the color filter 14 onthe substrate holding plate 2, the substrate fastening plate 5 is turnedrelative to the substrate holding plate 2 to hold fixedly the mask 8 andthe color filter 14 between the substrate holding plate 2 and thesubstrate fastening plate 5. In this state, the color pattern films 10of the color filter 14 coincide with the openings 8 a of the metal mask8, respectively. The metal mask 8 is attracted by the magnets 6 of thesubstrate fastening plate 5, so that the metal mask 8 is pressed firmlyagainst and held in close contact with the color filter 14. The gap 11is formed between the metal mask 8 and the peripheral portions (blackshading strips 10 b) of the color pattern film 10 of the color filter 14by the stepped portion 8 d formed in the brim portion 8 c of eachopening 8 a of the metal mask 8, and the metal mask 8 is connectedelectrically to the peripheral portions (black shading strips 10 b) ofthe color pattern films 10 of the color filter 14 by the conductiveprojections 12. The metal mask 8 and the color filter 14 may be providedwith locating holes at positions corresponding to the guide pins 7 tolocate the metal mask 8 and the color filter 14 accurately on thesubstrate holding plate 2.

The color filter 14 held by the jig 1 with the black shading strips 10 bof the color pattern films 10 of the color filter 14 electricallyconnected to the conductive projections 12 is placed in a processingvessel of a sputtering apparatus and an indium tin oxide film (ITO film)is deposited on the color filter 14 through the metal mask 8 to form thetransparent electrode layer 13.

Since the metal mask 8 and the glass substrate 9 of the color filter 14are connected electrically by keeping the conductive projections 12 incontact with the black shading strips 10 b, any potential difference isnot produced between the metal mask 8 and the glass substrate 9 of thecolor filter 14 due to the accumulation of charges. Therefore, it ispossible to prevent the formation of breaks in the black shading strips10 b of the color pattern film 10 due to dielectric breakdown caused byabnormal discharge.

Although the invention has been described in its preferred embodiment,the present invention is not limited thereto in its practicalapplication and various changes and variations are possible therein. Forexample, conductive projections may be formed on the color filter 14instead of the conductive projections formed on the metal mask 8. Moreconcretely, conductive projections may be formed on the black shadingstrips 10 b contiguous with the peripheries of the color pattern film 10by a film forming process for forming a film on the black shading strips10 b. It is preferable that the conductive projections are formed atleast at three positions in the peripheral portion of each color patternfilm 10.

What is claimed is:
 1. A sputtering mask for forming a transparentelectrode film on a color filter by sputtering, said sputtering maskcomprising: a mask body provided with an opening having a shapecorresponding to that of a color pattern film of the color filter, and agap forming portion formed by recessing a brim portion of the openingfacing the color filter; and a conductive part formed in the gap formingportion so as to be in electrical contact with a conductive shadingstrip formed in a peripheral portion of the color pattern film.
 2. Thesputtering mask according to claim 1, wherein the gap forming portion isa stepped portion extending along the brim portion of the opening of themask body.
 3. The sputtering mask according to claim 1, wherein theconductive part is a conductive projection projecting from the gapforming portion of the mask body.
 4. A sputtering method of forming atransparent electrode film on a color filter by sputtering, saidsputtering method comprising the steps of: preparing a sputtering maskprovided with an opening having a shape corresponding to that of a colorpattern film of the color filter; placing the sputtering mask on thecolor filter so that the opening of the sputtering mask coincide withthe color pattern film and a gap is formed between a brim portion of theopening of the sputtering mask and a peripheral portion of the colorpattern film of the color filter; and forming a transparent electrodelayer by sputtering using the sputtering mask on the color filter withthe sputtering mask electrically connected to a conductive shading stripformed in the peripheral portion of the color pattern film by aconductive part.